Intra-sector sub-sector wear leveling for memory reliability
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Solution Overview
Problem
Traditional wear leveling techniques in memory devices fail to effectively account for sub-sector wear, especially in high data cycling applications like page-flash implementations, leading to premature failure due to uneven usage of memory cells.
Innovation Solution
The implementation of sub-sector wear circuitry that performs intra-sector swaps, where data is moved from high-wear sub-sectors to low-wear sub-sectors within the same sector, along with additional logic to prevent over-cycling and reduce silicon area usage through intra-sector bundling and rescrambling circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional wear leveling techniques are used, then data is spread across sectors, but sub-sector wear is not effectively accounted for leading to premature failure
Solution Approach 1:
The patent divides each sector into multiple sub-sectors (e.g., 4 sub-sectors per sector) and independently tracks wear cycles for each sub-sector. This segmentation allows the wear leveling algorithm to operate at a finer granularity, moving data between sub-sectors within the same sector to equalize wear distribution. The block mapping unit maintains separate cycle counters for each sub-sector, enabling precise wear monitoring and effective load balancing without requiring cross-sector operations.
Solution Approach 2:
The patent introduces a new dimension of wear management by implementing sub-sector level granularity within the existing sector structure. Instead of only moving data between sectors (one-dimensional approach), the system now operates within the intra-sector dimension by selecting specific sub-sectors for data placement based on their individual wear states. This additional dimensional layer enables more sophisticated wear distribution while maintaining sector-level organizational structure.
2Reliability
If data is moved between sub-sectors to equalize wear, then sub-sector wear is balanced, but hardware overhead and processing time increase
Solution Approach 1:
The patent segments the memory hierarchy into block, sector, and sub-sector levels, with the block mapping unit managing wear leveling at the sub-sector level within each sector. This segmentation allows the system to track and balance wear at the most granular level (sub-sector) while maintaining higher-level organizational structures (sectors and blocks) for efficient address management and data retrieval.
Solution Approach 2:
The system performs preliminary wear tracking and sub-sector selection before actual data write operations. The block mapping unit pre-calculates the optimal destination sub-sector by comparing wear cycle counts, and prepares the address mapping in advance. This preliminary action ensures that when data needs to be written, the system can immediately direct it to the least-worn sub-sector without requiring complex real-time decisions during the write operation itself.
Solution Approach 3:
The patent implements a feedback mechanism where the block mapping unit continuously monitors wear cycle counts for each sub-sector and uses this information to dynamically adjust data placement decisions. After each program operation, the system updates the cycle counters and uses this feedback to make informed decisions about future data placement, ensuring that wear is evenly distributed across all sub-sectors over time.
Data Source
AI summary
Systems and methods for intra-sector re-ordered wear leveling include: detecting, in a memory device, a high wear sub-sector having a high wear level, the sub-sector residing in a first sector; determining a second sector of the memory device having a low wear level; swapping the first sector with the second sector; and re-ordering a position of at least one sub-sector of the first sector, the second sector, or both.